Water wells containing potable water require periodic cleaning in order to remove scale from the well casings, well screens, pump bowls, etc. Typically, this scale is removed using an acid solution, generally a solution of hydrochloric acid. However, when such acid cleaning agents are used, several of the components forming the pumping mechanism are subject to attack by the acid, in particular, the well screen which is usually made of 304 stainless steel, the well casing which is usually made of mild steel, and especially the pump bowl which is usually cast iron. The hydrochloric acid is usually present in the cleaners in a concentration range of from 10 to 20% by weight which, upon repeated use, can be quite damaging to the above parts. In order to protect these parts from the acid during the cleaning cycle, inhibitors have been added to the acid cleaning mixtures. However, these inhibitors have generally been of two types, namely, a toxic inhibitor such as diethylthiourea or the nontoxic inhibitor gelatin, generally that manufactured under the tradename "Knox". The use of toxic inhibitors is, of course, quite undesirable, while the use of gelatin is also unsatisfactory due to the difficulty of dissolving the gelatin in the cold water and the fact that the gelatin may not properly protect the metal parts of the well and especially the cast iron pump bowl. There is therefore a compelling need for an inhibited acid solution for cleaning potable water wells in which the inhibitor is substantially nontoxic, effective, and readily soluble.
The use of proteins such as gelatin to inhibit the corrosion of metals in acid solution is well known; see, for example, M. N. Desai et al, Werkstoffe Korrosion 14, 739-42 (1963) which describes the use of gelatin to inhibit the organic acid corrosion of brass. M. N. Desai et al, J. Inst. Chem. Calcutta 1973, 45, Part IV, 135-7 describes the use of gelatin as an inhibitor to protect aluminum alloys against acetic acid and chloro-substituted acetic acids. J. D. Talati et al, Vidya, 1969, 12(2), 182-192 discloses the use of gelatin to reduce the corrosion of aluminum and aluminum magnesium alloys when exposed to organic acids. K. C. Koshel, Australas Corros. Eng., August 1974, 18(8), 17-19 describes the use of caseinium purum gelatin, etc., to prevent weight loss due to corrosion of aluminum in hydrochloric acid. J. D. Talati et al Acta. Cienc. Indica., 1976, 2(3), 219-225 describes the use of inhibitors such as gelatin to prevent the corrosion of aluminum alloys in chloroacetic acids.
A number of patents and publications describe the use of gelatin as an inhibitor against the corrosion attack by acids on iron or steel substrates. British No. 1,052,771 issued to Pyrene Company, Ltd. on Dec. 30, 1966 describes the use of gelatin with inorganic acids, such as phosphoric acid, to inhibit corrosion on iron or steel. S. M. Beloglazov, Uchenye Zapiski Permsk. Univ. 13, No. 3, 85-92 (1959) describes the use of inhibitors such as gelatin and casein to protect steel against sulfuric acid. Willibald Machu et al, Werkstoffe Korrosion, 13, 745-752 (1962) discloses the inhibition of acid corrosion in 1N sulfuric acid by the addition of gelatin to protect a number of metals including iron metals, S. M. Beloglazov, Uch. Zap. Permsk. Gos. Univ., 19, No. 1, 37-41 (1961) discloses the use of agents such as gelatin and casein in acid solutions to prevent hydrogenation and a change in fatigue strength of steel. C. Cabrera et al, Cuba Azucar, 1977 (April-June), 13-20 describes the use of both treated and untreated molasses to protect steel against corrosion during the acid cleaning thereof. C. Cabrera et al, Cuba Azucar, 1976 (July-September), 20-26 describes the use of distillery slops for preventing the acid corrosion of steel. The use of hydrolyzates of gelatin to protect certain metals from acid corrosion has also been described. For example, Shiga, Shoji, Japan. Kokai, No. 74 35 244, issued Apr. 1, 1974 describes the use of gelatin or its hydrolyzate to prevent the acid corrosion of copper zinc alloys. U.S. Pat. No. 3,505,184 issued Apr. 7, 1970 to Gilbert J. Schaedler et al describes the use of hydrolyzed protein as an inhibitor in a zinc electrodepositing bath. Japanese Patent No. 49,035,244 issued Jan. 4, 1974 discloses the use of gelatin or its hydrolyzate to prevent corrosion loss from copper zinc alloys. Czech. Application No. 153,709 published June 15, 1974 discloses the use of protein hydrolyzate to inhibit the corrosion of steel in 39% HCl.